Drought

Drought is an extended period of exceptionally low precipitation. A
drought can feature additional weather characteristics, including high
temperatures and high winds.

Although low precipitation (rain, snow, or sleet) marks both droughts and
deserts, the two are different. A desert is a region that experiences low
precipitation as an everyday occurrence. A drought, on the other hand, is
a temporary condition in which precipitation is abnormally low for a
particular region. Droughts may occur at any time in any part of the world
and last anywhere from days to weeks to decades.

The U.S. National Weather Service recognizes three categories of drought.
A dry spell occurs when there is less than .03 inch (.08 centimeter) of
rainfall during a minimum of 15 consecutive days. A partial drought occurs
when the average daily rainfall does not exceed .008 inch (.02 centimeter)
during a 29-day period. An absolute drought occurs when there is no
measurable rainfall over a period of at least 15 days.

The intensity of a drought may be measured by the ability of living things
in the affected area to tolerate the dry conditions. Some plants quickly
fall prey to droughts while others, such as cacti and mesquite trees,
survive dry conditions by either storing water in their tissues or by
going dormant (a state in which growth activity stops). Although a drought
may end abruptly with the return of adequate rainfall, the effects of a
drought on the landscape and its inhabitants may last for years.

History

Droughts have taken place around the world throughout history. Some
scientist theorize that droughts brought about the migrations of early
humans. From 1876 to 1879, severe droughts in China caused the deaths of
millions of people from lack of food. In 1921, a drought along the Volga
River basin in Russia led to the deaths of almost five million people,
more than the total number of deaths in World War I (1914–18).

The best-known American drought occurred on the Great Plains region during
the mid-1930s. Labeled the Dust Bowl, the affected area covered
almost 50 million acres in parts of Colorado, New Mexico, Kansas, Texas,
and Oklahoma. During this period, dust storms destroyed crops and buried
agricultural fields with drifting sand and dust. As depicted by American
writer John Steinbeck in his award-winning novel
The Grapes of Wrath,
many farm families had to abandon their land.

Drought and famine have severely affected areas throughout Africa.
Beginning in the late 1960s, in the Sahel region south of the Sahara
Desert in northern Africa, a prolonged drought contributed to the deaths
of an estimated 100,000 people. The region was struck again by drought in
the mid-1980s and early 1990s. War and drought in Ethiopia in the early
1980s brought about the starvation of an estimate one million people and
the forced migration of hundreds of thousands of others.

Drought combined with social unrest continued to afflict many countries at
the beginning of the twenty-first century. The African nations of
Djibouti, Eritrea, Ethiopia, Kenya, Somalia, and Sudan were all hit hard
by a massive drought that began in the late 1990s. Conflicts like the

A dust storm approaching Springfield, Colorado, that would engulf the
city in total darkness for almost an hour. Dust storms can occur when
soil not securely anchored by vegetation is dried out by drought then
blown up by winds.
(Reproduced courtesy of the

Library of Congress

.)

border war between Eritrea and Ethiopia slowed the delivery of famine aid.
Devastating civil wars also worsened the effect of drought in the
countries of Afghanistan and Tajikistan. The unrelenting droughts were the
worst those countries had seen in decades.

The El Niño weather phenomenon typically brings about droughts in
various parts of the world as it disrupts normal weather patterns. Perhaps
one of the worst such droughts occurred in Southeast Asia as a result of
the 1997–98 El Niño period. The monsoon rains that normally
drench the area each September were delayed. Consequently, the jungle
fires set by farmers to clear land were not damped by the usual rain, but
instead raged out of control, propelled by hot winds. The smoke from the
fires hung over Southeast Asia like a thick, dirty blanket. It quickly
became the worst pollution crisis in world history. At least 1,000 people
died from breathing the toxic air; several hundred thousand more were
sickened.

Human impact on droughts

Soil that lacks humus (nutrient-rich material resulting from decaying
plants) and the binding property of plant roots cannot absorb or retain
moisture properly. Dry, crusty soil is easily moved by winds. The
overgrazing of farm animals, the overcultivation of farmland, and the
clear-cutting of forests all contribute to such soil conditions, adding to
the severity of droughts.